The investigations encompass a broad spectrum of structural research in chemistry and biochemistry. The unifying theme of the work is the need for detailed structural information on a variety of chemical species in order to elucidate stereochemical-functional relationships for the systems under investigation. X-ray crystallography can provide definitive information at high resolution about the detailed stereochemistry in three-dimensions of chemical and biochemical systems of interest. This detailed structural information may then be of crucial importance in understanding the reactivity, functional properties, and dynamics of the chemical systems. Areas of interest include nucleic acid structure and interaction with model probes, structural identification of transition metal complexes incorporating activated small molecules, model studies into potential metal binding sites, in molybdo- and cupro-enzymes, the elucidation of the stereochemistry of novel organic heterocycles possessing potential drug activity, and the structure and function of modified cytochromes, with emphasis on the dimensions of the heme-crevice and the effects of modification on redox potential. Single crystal x-ray diffraction has evolved into a necessary and routine structural tool which in conjunction with other physico-chemical techniques may yield definitive information on stereochemical and functional trends.